Adding a global legend to a tiledlayout

Good morning,

I'm using MATLAB R2020a Update 2. I have a tiledlayout of five (three by two) area plots and would like to use the sixth, currently empty, tile to add a global legend. I've already found this question, and understand that there's no official, built-in way of doing this, but perhaps it's possible to get creative.

What I've tried is adding a new, empty area plot to the sixth tile, using NaNs as the shares, then adding a legend to that and setting the axis object for that tile to invisible, as follows:

% ...
ax = nexttile;
area([NaN NaN], NaN(2, 4));
leg = legend({'tar', 'sta', 'ext', 'dmp');
leg.Location = 'none';
leg.Interpreter = 'latex';
leg.FontSize = 16;
ax.Visible = false;

This works in principle, but leaves a horizontal line where the X axis would be:

This only happens when I use area(), not e.g. plot(). Perhaps it's a bug, perhaps it's intentional and due to the way area() works. In any case it's not what I want, but I can't get rid of it (without breaking other things in the process).

I had the idea of making the children of this axis, i.e. the areas of the area plot, invisible as well, like so:

for i = 1:length(ax.Children)
    ax.Children(i).Visible = false;
end

But while this gets rid of the horizontal line it also grays out the legend entries:

This behavior in turn is known and expected and apparently cannot be changed. The workaround suggested by a Mathworks staffer in the linked question is to plot NaNs; but that's what I'm already doing and what's leaving the horizontal line, due to area()'s quirks.

Can anyone help?

I'm not hung up on specifically creating an invisible area(), this is merely the best (first, only) idea I had for fudging a global legend. If anyone can make this approach work, that'd be wonderful. If anyone has another idea of how to achieve a similar effect, that'd be wonderful as well.

Thank you very much!

Answer 1

[Rik]

I can't get the position quite right, maybe you have more luck with your tinkering. This at least gets rid of the line. (I guess this is what you meant with boiler plate code in your answer here)

The new tools (like tiledlayout) have some advantages over using subplot, but this hasn't convinced me so far.

rng(4);
figure(1),clf(1)
tiledlayout(3,2);
for n=1:5
    nexttile
    Y=rand(30,4);Y=Y./sum(Y,2);
    area(Y)
end

ax = nexttile;
p_ax=ax.Position;
area([NaN NaN], NaN(2, 4));
leg = legend({'tar', 'sta', 'ext', 'dmp'});
p_leg=leg.Position;
delete(ax)
ax=axes('Position',[p_ax(1:2) 0 0]);
area([NaN NaN], NaN(2, 4));
leg = legend({'tar', 'sta', 'ext', 'dmp'});
leg.Location = 'none';
leg.Interpreter = 'latex';
leg.FontSize = 16;
ax.Visible = false;
leg.Position=p_leg;

[Christian Schröder]

Excellent, that's great, thank you so much! I was able to put the legend more or less in the right place as follows:

fake_ax = nexttile;
ax_pos = fake_ax.Position;
area([NaN NaN], NaN(2, 4));
fake_leg = legend({'tar', 'sta', 'ext', 'dmp'});
fake_leg.Interpreter = 'latex';
fake_leg.FontSize = gp.axis_font_size;
leg_pos = fake_leg.Position;
delete(fake_ax);
ax = axes('Position', [ax_pos(1:2) 0 0]);
area([NaN NaN], NaN(2, 4));
leg = legend({'tar', 'sta', 'ext', 'dmp'});
leg.Location = 'none';
leg.Interpreter = 'latex';
leg.FontSize = gp.axis_font_size;
leg.Position = [(0.75 - leg_pos(3) / 2) (0.2 - leg_pos(4) / 2) leg_pos(3:4)];
ax.Visible = false;

This way the fake legend has the same size as the real one, and it's roughly centered.

And yes, this is one example of what I meant by "boilerplate code". (A while ago I also ran into trouble when trying to control the placement and formatting of tick labels; fortunately I was able to find what I needed on MATLAB Answers.)

Answer 2

[Adam Danz]

Update

As of Matlab r2020b, legend location can be specified relative to axes created within an TiledLayout. This demo below produces 1x4 tiles of axes and the adds a legend to the East of the layout.

% DEMO
fig = figure(); 
fig.Position(4) = 225; 
colors = [winter(3);summer(3);autumn(3);copper(3)]; 
subPlotNames = 'ABCD'; 
h = gobjects(3,4); 
tiledlayout(1,5)
for i = 1:4
    ax = nexttile;
    h(:,i) = plot([0,1],[.66;.5;.33].*[1,1],'LineWidth',4);
    text([.1,.1,.1],[.66;.5;.33],{'1' '2' '3'},'VerticalAlignment', 'Bottom')
    set(h(:,i), {'DisplayName'}, compose('%s %d',subPlotNames(i),1:3)')
    title(subPlotNames(i))
end
set(h(:), {'Color'}, mat2cell(colors,ones(12,1),3))
lg  = legend(h(:)); 
lg.Layout.Tile = 'East'; % <-- place legend east of tiles

[Christian Schröder]

Very cool! MATLAB just keeps getting better with each new release. Thank you very much!

Answer 3

[Rubens R. Fernandes]

I think I got a solution for this!

In my case, I am using a tiled layout of (2x2), and the legend is defined on the data plotted for the first layout.

What I got is:

figure

%Defines the variables
x=linspace(1,10,10);
y1=x;
y2 = 2.*x;
y3 = 3.* x;

%Initiates the figure
tiledlayout(2,2)

%Plots the data in tile 1
nexttile(1)
plot(x, y1, 'DisplayName', 'y1');
hold on
plot(x, y2, 'DisplayName', 'y2');
hold on
plot(x, y3, 'DisplayName', 'y3');

%Plots the data in tile 2
nexttile(2)
plot(x, y1.^2, 'HandleVisibility', 'Off');
hold on
plot(x, y2.^2, 'HandleVisibility', 'Off');
hold on
plot(x, y3.^2, 'HandleVisibility', 'Off');

%Plots the data in tile 3
nexttile(3)
plot(x, y1.^3, 'HandleVisibility', 'Off');
hold on
plot(x, y2.^3, 'HandleVisibility', 'Off');
hold on
plot(x, y3.^3, 'HandleVisibility', 'Off');

%Plots the legend in tile 4
ax = nexttile(1);
lg  = legend('Orientation','Vertical','NumColumns',2, 'Interpreter', 'Latex');
lg.Layout.Tile = 4; % THIS IS THE COMMAND THAT WILL SET THE TILE WHERE YOU WANT TO PLOT YOUR LEGEND

Hope it helps!

[Philipp Richard]

Awesome ! Thx !

[Christian Schröder]

This is also very cool, and for the record you can specify "south", "north", "east" and "west" instead of a tile number to place your legend outside of the grid of tiles in the tiledlayout as well.